1. Field of the Invention
The present invention relates to a tape rule with a lighting device, and more particularly, to an inexpensive, simply constructed tape rule containing a lighting device which can illuminate the scale on the tape by actuating an attached light emitting diode (LED) in case the measurement work is to be carried out in a dark environment or at night time.
2. Description of the Prior Art
The tape rule, though an old fashioned instrument, is still playing a very important role in civil, architectural engineering or the like. In many situations the measurement work has to be carried out in a dark environment such as at night time or in tunnels where no aid from an external lighting source can be depended on. The measurement work is carried out by the operator in such way that he must, with great difficulty, hold the tape rule in one hand, while carrying a portable light source such as a flashlight in the other hand to illuminate and read the scale on the tape. Under such a circumstance everybody would eagerly expect to have a tape rule having a light source therewithin.
There is a patented invention "A tape rule with lighting device using a printed circuit board switch" promulgated in ROC Patent No.92264, which discloses a movable actuator to drive a flexible and elastic printed circuit board on which a contactor pad is located, and by displacing the contactor pad the lighting device is connected to a power source so as to turn on the light for illumination. Though this cited case successfully introduced a light source to a tape rule, it is too complicated in construction. Use of excessive amount of components disposed in a small tape rule incurs a high fault rate as well as increased production costs for the tape rule.
Another patented invention "A tape rule with lighting equipment" was promulgated in ROC Patent No.82802 which discloses inclusion of an eccentric wheel to push a copper contactor strip, which causes an LED to be turned on to emit light. However, the second cited case has similarity in every respect with the former one in that too many components are involved. The two cited cases mentioned above are by no means to be considered perfect.
In order to cope with this situation, research and development has been carried out by the inventor of the present invention, so that the inconvenience and disadvantages inherent to the conventional techniques as mentioned above can be eliminated.